Cast pigmented plastic sheet



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2 fgj 2 5 M 4,2 ggg Oct. 28, 1952 which there are grades,somerdifferingas to properties, chemical 4-fcomposition and: molecular weight, will.bere- Patentecl ct. 28, 1952 marmi-'D STATES Para NT lof-FFrela;

'-'CAST PIGMENTED PLASTIC 'SHEET William WalterfUlmer, Alexandria,l andLouis R. Burroughs,` South Bend,"Ind.;^said-'-Bur roughs assignerto saidUlmer 'Application January 30, 1%8, Serial No. 5,287

" 1"'Claim. 1 This iinvention -relates to 4improvements in plastic ylm.

Thevprimary-object of the invention is to provide aplastic film,-whichmay be made of `diiferent thicknesses, .in different-patterns, and tov.possess a-wide range of various other properties offphysical anddecorative character.

A further object is to provide aplastic lm havingAcertain-characteristicdesigns which can`v be `selectively Iprovidedtherein4 duringormation `thereof and whichfimpart theretonoveldecorative and lcamouflaging= effects.

-Avfur-therobject is .to provide a novel..method for vintroducingadesign in a' plastic lm.

, Other" objects Will be apparent from.the descriptiOn,` .drawings andappended claim.

, .In .the drawings:

Figs. 1 to 3, inclusive, .are face viewsof a frag- A.mentof ai filmhaving different. characteristic designs or patterns.

. Fig. rl is a perspective-view of a patterned film. Eig. 5 is a view ofone. form of yapparatus for l .producing the 'plastic film.

6 is a view of a diierent'film-forming appa- .ratus.

` Fgl '7 is a view'o'fv a third vtype of 'film-forming apparatus.

-'.Y Fig. Sis aldiagrammatic view of ianother type ".ofQlm-formingapparatus.

Fig. 9 is an 'enlarged sectional View `of a nlm. Fig."l isan enlargedsectional Viewof a nlm i' illustrating the manner in which pigment'isconcentrated at the design-or pattern-forming areas of the film orsheet.

This application is acontinuation inpart of our co-pending application,Serial No. 556,462,

'.led September29, 1944, now abandoned.

' The plastic lms toA which' this invention relates are very thin lmspossessing"'waterproof propertiesand at least a limited vdegree ofelasticity. 'They may be used for many purposes,

A.some of 'which are bathing caps, moisture seals Vfor Velectricinstruments, diaphragms for low pressure y tains', 'packaging' orwrapping -materiaL and rthe like.

measuring instruments, shower cur- Preferably they are formedvessentially of natural or 'syntheticlmateriala such as polyvinyl"-chloride, polyvinyl `chloride-acetate copolymer, celluloselacetate'andv cellulose nitrate. Films of synthetic rubber formed bydipping, and lms of -latex formed by dipping, are also contemplated lwithin the scope of the invention. For purposes ofl simplication, thesematerials, of some of afnumber of different types or 2 `ferred to.herein. as synthetic "resins, It'willfbe understood, however, that4there are-manyother vsynthetic resins than those" specically-f'imen-.tioned above from. which,by mixture'withplasticizers and 'solventstherefor',"andgbydippingr of a form or spreadingon'a form, a lm'may-beproduced, :and therefore the `invention-will "befunderstood to apply'tothemas well as the-materials named speci'cally'herein. Alsorthevlm mayconstitute a'coatingof syntheticrresin-'applied to a base; such vas apaper; cloth `or -brous sheet and adheredtheretd as-by` partialforcomplete impregnation'of said-sheetbythe-synthetic resin.

' Theproperties'fof a1 lm produced `from a synthetic'resin depend uponthe individual? char- 'acter ofthe Specic `base material employed,

upon the y nature and proportion of aiplasticizing materialusedthere'w-ith, and uponfthe-:nature andamount of the-solvent4usedfftherewith.

These materials must beV Vso mixed that the :re-

' sulting 'mixture' is^uniform throughoutliandgs inthe-nature of acolloidal suspensionf-:Fo'rbest results the` nlm-formingvmaterialfflsliouldisvbe stable, i. e. shouldy not be vsubject toprecipitation lof solids. -Any departure from auniformstable lconditionof the nlm-forming .material wil-laresult in the production of films1therefrom which lackuniformity ofthickness and other...charac teristicsand properties ,-desired.

We-have ldiscovered that a .stable =film+iorming material can beproducedbymixingzthe synthetic resin, plasticizer and Asolvent in desiredproporv tions-,and vcookingv the .mixture at atempera'ture `just under Athe boilingzpoint of i .the y'solvent :for

an extended periodl of =time during whichthemx- -ture iscontinuouslystirred. 'One examplefisto miX 32 gms. of polyvinylrchloride-.acetatecopolymer in the vgradesrof f heaviest molecular vweight with 20 gms-of a plasticizen. such `asrdioctyl phthalate ortricresyl phosphate.; and--fwith two `pounds 'of a solvent suchasvmethyl rethyl ketone.v If such amixtureis cooked at. antemperature offrom 140 F.tof160"F..for :l1/2.'.hours with continuous stirring, a-stablecolloidal'a'dispersion of `the resin and the plasticizerin'zthe'sol- 1 -vent is obtained. The nlm-forming. mixture:` so`prepared will stand for longperiodsof` time vvithlout noticeableprecipitation. 1 Also; stirring of this mixture during the operation-offorming a vfilm is substantially or practicallyavoided.v It will beunderstood, however, that thev above preparationl and `treatment isillustrative, and .that

the-treatment used will vary with' the composition-andcharacter of thesynthetic,V resin and of the particular plasticizing material andsolvent used.

There is a substantial range of the proportions in which the constituentmaterials may be mixed. The proportions given above are intended for theproduction of a very thin lm. However, the proportions may be varied byeither reducing or increasing the amount of the resin employed, reducedamounts of resin used resulting in thinner lms and use of increasedamounts thereof producing a thicker nlm.

The lm may be made with apparatus of the type illustrated in Fig. 5. Acontainer 2l) open at its upper end contains a quantity or bath 2l ofthe synthetic resin nlm-forming liquid described above or any otherliquid material from which a film of the type mentioned above may beformed. A frame 22 extends above the top of container 20 and journals apulley 23. A plate 24, preferably formed of glass or other materialhaving a very smooth surface, may be supported in vertical position by abracket or clamp suspended from a cable 26 or the like trained aroundthe pulley 23. Suitable means, here illustrated as a drum 2l journaledin a bracket 28 and operated by a crank 30, are provided to play out andpull upon the cable to lower the plate 24 into the bath and withdraw itfrom the bath. It may be mentioned also that if the plate 24 is formedof metal, it should be chrome or nickel plated to prevent chemicalreaction with the bath 2l. Plate 24 may also be made of aluminum if thesame is provided with a highly polished surface.

The operation of forming the film with the apparatus described above saccomplished by lowering the plate 24 into the bath 2l and thenwithdrawing said plate at a uniform speed. Control of the speed ofwithdrawal of the plate is critical to both uniformity of the filmproduced and the thickness thereof. Thus, if a mixture prepared in themanner and of the proportions described above is withdrawn very slowly,at a rate not faster than the rate at which the mixture will flow, forexample at a rate of about 41/2 inches per minute, a nlm 30 of minimumthickness, i. e; in the order of a thickness of .004 inch will beproduced upon the surfaces of plate 24. Withdrawal of plate 24 from thesame solutio-n at a faster rate will produce a thinner film 30 uponplate 24, for example, withdrawal at the rate of about 36 inches perminute producing a film in the order of .0012 thickness. For any givenmixture there will be a minimum and a maximum film thickness obtainable.Thicknesses between these limits can be obtained by proper timing of therate of withdrawal. Therefore, two factors control nlm thickness, i. e.,the consistency of the bath and the rate of form withdrawal. Hence it ispossible to produce a lm of any of a wide range of thicknesses and awide range of properties, such as elongation, resilience and the like.The lm can be stripped from the form easily, since it has only africtional adhesion therewith, and its elasticity and exibility assistin the operation of peeling it from the form. The thinness of the nlmfacilitates the drying action.

The temperature at which the bath is maintained is not critical with thepolyvinyl chlorideacetate copolymer mentioned above, and satisfactoryresults can be obtained, without detrimental efect upon the propertiesof the bath, if the same is maintained at any temperature which is belowthe boiling point of the solvent and above the solidifying point of themixture.

" Thus the operation can be conducted to produce a satisfactory nlm attemperatures as low as -20 C. and as high as 79 C., with the mixturedescribed above. Temperatures in the upper part of this range arenaturally preferred. The temperatures employed with other of thesynthetic resin materials will depend upon the properties thereof and ofthe plasticizer and solvents used therewith, as is well understood inthe art.

The lrn produced by the above method will be of uniform thickness andclear and transparent, if the constituent materials are not pigmented.Colors can be incorporated as desired, as by using pigmented syntheticresin. Different degrees of opacity can be obtained by incorporatingtalcum powder, talc, flour or like materials in colloidal suspension inthe film-forming bath. The film may posses other properties, such asflexibility, elasticity, uniformity, water-proofness or moistureresistance, depending upon the synthetic resin employed.

The method of forming the lm may be altered from that described above toone wherein the mixture is poured upon a horizontal form and thenleveled and its thickness regulated by the use of a scraper, after whichthe film is permitted to set and dry. The latter method may be practicedby either of the types of apparatus shown in Figs. 6 and 7wherein thehorizontal forming plate is illustrated at 35, and also may be practicedby forming a nlm on a web or belt in a continuous process, as shown inFig. 8. -The advantage of these methods lies principally in theiradaptation to the provision of design patterns in the nlm being formed.Thus, referring to Fig. 6, the plate 35 is mounted on a suitablehorizontal support 36 in which is journaled a shaft 3l driven by anelectric motor 38. Cams 39 may be mounted on shaft 3l of such size andshape that they engage and vibrate the plate 35 ata predetermined orselected period. While one shaft 37 mounting two cams 39 has beenillustrated, it will be understood that a plurality of cam shafts may'fbe employed, operating at the same or different speeds depending onthe design pattern desired, that each shaft may mount one or anyselected number of cams, and that the cams may be of the same contour ordifferent contours depending upon the design pattern desired. ,'In theapparatus shown in Fig. 7, the plate 35 rests upon support 36 and isengaged by the spring'pressed armatures 40 of solenoids 4l or otherelectrical apparatus such as a magnetic vibrator of the type used inloud speakers. While two solenoid armatures are shown, one, or more thantwo, may be used if desired. The units 4l may be controlled forvibration thereof or of the armature thereof at high frequency by aconventional audio oscillator 42 which is preferably of the type whosefrequency can be regulated.

In the apparatus shown in Fig. 8, an endless web or belt 6G of anysuitable material is' trained around rollers 6l, one of which ispreferably power driven. The upper run of the belt has the fluidsynthetic resin applied thereto at 62, as by flowing the same thereonfrom a container 63. The resin coating is smoothed and its thicknessregulated by suitable means such as rollers 64, S5. Thereafter the beltis acted upon by one or more vibrators 65 while it is solidifying andsetting. The completed film v66 is separated from the belt, as byscraper 6l, after it has dried or set, and is then rolled at 68, orotherwise handled.

When a nlm is formed on any of thejdevices shown in Figs. 6, '7 and 8,or on a device such as shown in Fig. 5 which is provided with suitableyr'neansl (not shown) 'for'vibratingthe' plate l2li as'it is withdrawnfrom bath 2|, or on any other suitable apparatus provided 'withvibrating means, certain properties of the nlm result. The

-film assumes adennite vpatterned or design appearance as the result ofthe vibration. Characteristic design patterns are'illustratedA in Figs.

1, 2, 3 and 4. It' will beunderstood, of course,

that the designs'illustrated in said Figs. l to 4 of darker'and lightervvshades of the same color,

as illustratedin Fig. v'10 'where the spacing'of the dots isindicative-of the concentration of the pigment. In exceedingly .thinnlms or any film which is translucent and normally transparent, theseproperties are-retained in the designed or patterned nlm, but the'designbreaks the continuity of an image viewed therethrough by an effect uponthe eye which can be-likened to that of camouflaging. These properties,therefore, offer substantial possibilitiesA in decorative and otheruses. The vibration preferably occurs as the film is being dried, andinmost cases. entails al certain degree of thickening of the film atvthe patternforming lines or areas. This is not noticeable in thin nlmswhich have been vibrated at-highfrequency, but increases as nlmthickness and amplitude of vibration increase andas the 1 frequency ofvibration decreases.

The process of forming a design upon synthetic resin nlm is not limited-to performance at the time when the nlm is being formed. Thus apreformed nlm may be treated -to impart a design thereto. Such treatmententails softening Yat least the surface portion of the preformed nlm torender the same fully or partially fluid, as by applying a solventthereto or by the combined action of heat and a solvent. When the nlm ornlm surface has been softened or rendered nuid to a degree to permit itto be reworked or reshaped, it can be subjected to vibration by anylsuitable means during the time the solvent is evaporating and the nlmis setting to self-sustaining condition, i. e., until its shape or formcan no longer be varied or until it will retain its shape or contourunless forcibly reshaped. In this connection, nlms of the type known inthe art as dipped nlms or cast or molded films can be readily worked bythis method. Some other types of nlms, and particularly those known inthe art as calendered nlms, present greater difnculties to and are lesswell adapted for practice of this method thereon after the same haveonce been formed.

The time at which and during which vibration is applied in the processof forming a film, as shown in Figs. 5, 6, 7 and 8, is governed by thesame considerations mentioned above. In other words vibration mustcommence while the nlm contains some of the solvent and possesses atleast a measure of free fluidity and must continue until enough of thesolvent is evaporated so that such nuidity ceases and-the film becomesselfsustaining or shape-retaining, and preferably until it is no longerworkable or until it can only be worked by application of substantialforming pressure thereto.

' ned than thinner films.

Vibration within aw-iderange-of `frequencies may be appliedto produce adesign-pattern asdescribed above. V'Iherange-of frequenciesfeffectivetoproduce a design varies from-alow=limit of approximately 200cycles-persecond-to'ahigh limit of approximately 30,000 cycles Y-persecond. The pattern produced varies withr-the-frequency, and Fig. 3 isillustrative'of a coarsepatternproduced at low frequencies; Fig. 2isillustrative of a nnepattern produced at high frequencies;- and Fig.lis comparatively illustrative ofapattern produced at an intermediatefrequency. -fThe pattern-will vary somewhat V,with the `Vthickness ofthe nlm, particularlywhere -the'amplitude `of vibration at agivenfrequencyY remains constant when applied to nlmsof Vthe samelmaterialbut of' different thickness. In general, however, if amplitudeof vibration is increased proportionally to increases in filmvthickness, vthechange of 4design for a given frequency upon nlms ofthesame material but of different thicknesses will be small. Thethickness of the nlm may vary from approximately '.002l inch to'`yapproximately -.()12 inch. Films of thicknesses Ygreater than'thelatter'limit donot offer a satisfactory basis for the-practice of themethod under all conditions, althoughthey are not completely devoid ofpropertiespermitting practice ofthe method. Also, nlms at or near theupper limit 'of thickness generally'are less susceptible of designing'atfrequencies at or near the upper end vof the frequency range'speci- Thegreatest variation of design pattern occurs at the lower frequencies;thus at frequencies exceeding .116,000 cycles .per second, very-largedifferences in frequency 'are required to produce substantial orappreciable differences in design.

As mentioned above, the vibration method mayv be practiced upon sheetmaterial coated with a thin nlm of the synthetic resin.V Thesheet'material may be paper, cloth or other' fibrous sheet material towhich the synthetic resin adheres or which is partly or completelyimpregnated or saturated by the synthetic resin. Such material may bevibrated in any manner suitable, and in cases where the coatingthickness is Within the range specified and the vibration applied iswithin the range specified, and is of suflicient amplitude and duration,the production of a design will result.

The vibrated nlm, in addition to its design, will also be characterizedby a rippled surface at the face thereof opposite that which bearsagainst the form or support, as best seen in Fig. 9, or at the coatingsurface or coated sheet material. This can readily be detected in thecoarse patterns, especially where the amplitude of vibration has beensubstantial, and becomes less noticeable as the pattern becomes nner.Such ripples obviously entail the formation of surface ridges anddepressions, and therefore the thickness of the film varies from pointto point, although the differences will usually be very small and willnot appreciably reduce the strength of the nlm or be otherwisedetrimental.

Synthetic resins of the types described above may be plasticized byother materials than those mentioned above. The proportions in whichsuch other plasticizers are used will depend upon the synthetic resinwith which they are used, as is well understood in the art, anddifferent plasticizers may be found to be preferable to secure differentcharacteristics which it is desired to obtain in nlms made fordifferent. uses and purposes. Different solvents from that specincallymentioned above may also be used. The proportions in which differentsolvents are incorporated will depend essentially upon the molecularweight or specic gravity of each solvent and on the synthetic resin andplasticizerv with which each is used. Invgeneral, as the specificgravity of solvents increases, an increase of the amount of solventproportional to the percentage of increase in the specific gravity mustbe supplied.

Synthetic resins of the type described above may also be mixed withother resins and synthetics. The test of the materials so usable appearsto be whether or not such materials are compatible with the syntheticresins. Tests made adding to polyvinyl chloride-acetate copolymer adifferent synthetic resin, such as methyl methacrylate, and to syntheticrubber materials as Buna S and Hycar show that they are compatible. Thematerials listed will be understood to be illustrative and not to becomplete. The properties of the film diier according to such othermaterials added to and forming part of the nlm-forming bath, among whichmay be mentioned drying characteristics and different degrees ofelasticity. Hence, for a given use, where certain properties areessential, the nlmforming bath may be formulated by variation of theillustrative formula given above to provide such properties in the film.Also, it has been found that the design patterns resulting fromvibration dier with the different synthetics incorporated in thenlm-forming liquid. In other Words, a material containing methylmethacrylate and polyvinyl chloride-acetate copolymer, when processed toa given lm thickness and vibrated at a given frequency, will have adiiferent design pattern than a material containing polyvinylchloride-acetate copolymer only when processed to the same thickness andvibrated at the same frequency.

In the manufacture of lhns in the manner described above, the lm doesnot become stable until it has been dried thoroughly; that is, until thevolatileconstituents of the film-forming material have been evaporatedor expelled. The

nlm is subject to shrinkage and has an odor' characteristic of thevsolvents, until it becomes stable. In the thin sections of the order towhich reference has been made, complete drying can be accomplished bysimply exposing it to atmosphere. However, complete elimination orevaporation of volatile constituents by air drying is slow. rI'herefore,it is preferable for practical considerations toy pass the lm through aheated chamber or otherwise subject it to heat to accelerate expulsionof Volatile constituents in most cases.

We claim:

A cast synthetic resin sheet of substantially uniform thickness andcontinuous integral structure, said sheet being pigmented throughout andbeing characterized by greater density of said pigment at some partsthereof than at others to denne a design pattern, one surface of saidsheet being rippled with the ripples thereof coinciding with the partsof greatest pigment density.

WILLIAM WALTER ULMER. LOUIS R. BURROUGHS.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 596,942 McGowan Jan. 4, 18981,806,863 Paissean May 26, 1931 1,886,972 Payne Nov. 8, 1932 1,950,417Root Mar. 13, 1934 2,238,730 Hauffe Apr. 15, 1941 2,304,632 Faelten Dec.8, 1942 2,360,650 Crane Oct. 17, 1944 2,371,868 Berg Mar. 20, 19.452,440,039 Brown Apr. 20, 1948 2,480,749 Marks Aug. 30, 1949 FOREIGNPATENTS Number Country Date 711,683 Great Britain Sept. 15, 1931

